The mission of the Body Composition and Energy Balance (BCEB) Core is to support investigations of the metabolic causes and consequences of obesity and of other nutritional disorders, and the effects on body composition. This core, like the Pittsburgh ONRC in general, is principally, though not exclusively, designed to support clinical investigations, provides equipment, scientific and technical expertise, and a portfolio of methods and services for ascertaining body composition, in vivo metabolism, physical activity and fitness, and energy balance. This core has the range to support clinical investigations of body composition, substrate metabolism and energy balance at an organ-specific level, as well as at the whole body or systemic level. Additionally, through close interaction with the Laboratory, Core, particularly the newly established Metabolic Laboratory, human investigations of tissue composition and metabolism can be taken to a cellular level, using biopsy material. Another initiative takes the capabilities of the BCEB in the opposite direction, that of flee-living, community based assessments of physical activity, collating within this core the accumulated experience and expertise of a range of assessment questionnaires developed and tested in numerous special populations. A key theme across the components of the BCEB core is to study insulin resistance and the relation to adiposity. The Body Composition and Energy Balance Core seeks to fulfill its mission not only through the facilities of the ONRC, but also by partnership with both the pediatric and adult GCRC at the University of Pittsburgh, and with centers for in vivo bio-imaging, including positron emission tomography (PET) and nuclear magnetic resonance (NMR/ MRI).